A switching-mode power supply (SMPS) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. Like other power supplies, it transfers power from a source to a load while converting voltage and current characteristics. Unlike a linear power supply, the pass elements of a SMPS continually switch between low-dissipation on and off states. Depending on the amount of current flowing in the switching elements during commutations SMPSs can be classified as Hard-Switching and Zero-Current-Switching.
In a Hard-Switching (HSW) topology switches are turned on/off while the converter is still delivering current to the output, this means that they spend some time in high-dissipation transition states. Since this time is usually small (10 ns range), efficiency loss is acceptable as far as input voltage, for a given load, is low (12V-16V).
The picture changes when dealing with high input voltages (40V-60V) since losses due to hard switching have a relevant impact on efficiency. For this reason Zero-Current-Switching (ZCS) configurations have been proposed in order to minimize power losses during transitions. These converters are usually based on resonant LC cells where the switching events needed to redirect energy from input to output are synchronized with LC oscillations.
From above description it is evident that while in a HSW converter switching events (duty cycle) can be freely controlled to get a desired Input-Output ratio, in a ZCS converter this is no longer possible since switching events are constrained by the resonance. For these architectures conversion ratio is usually defined by means of external components and cannot be changed.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.